Sea Anemones

It is often thought that they are plants because of their name, but sea
anemones are animals and in fact, they can be quite aggressive, being
predatory by nature. Their name actually originates from the shape of
their mouth, surrounded by tentacles, which together are said to
resemble the flower of an anemone in appearance.

At least 9,000
different sea anemones can be found in the world’s oceans, with the
majority living in tropical waters. A number of these are free-swimming,
at least for a stage in their life cycle. They then anchor themselves
to rocks and other similar underwater sites. Here they rely on their
stinging tentacles to capture small invertebrates and fish on which they
feed.

The beautiful and sometimes bizarre appearance of sea
anemones has been a source of fascination to marine aquarists for many
years but only recently has there been the available technology to
enable them to be kept and studied in a home aquarium. Although still a
specialist branch of fish-keeping, tanks housing ‘invertebrates’ with
few, if any, fish present, are growing in popularity now.

Back in
the early 1960s, it became clear that rocks which already supported
marine life were essential to the success of this type of aquarium. The
term ‘living rock’ entered the vocabulary of marine fish-keepers during
this era. While many marine aquarists concentrated on the quality of the
artificial sea water in such systems, it became clear by the 1970s that
lighting was also highly significant to keeping sea anemones, corals
and similar creatures successfully in these surroundings.

Importance of correct lighting

A high
light intensity in the aquarium ensured the development of the marine
algae. In the same way that most household plants will not grow in the
dark, so these algae will fail to thrive, requiring light for the
process known as photosynthesis. Certain algae are also to be found
within the body of many anemones and are vital to their well-being. It
seems that these primitive plants help to provide some of the sea
anemone’s nutritional needs but the precise nature of their relationship
is still unknown.

Without this algal presence however, the
health of the sea anemones will suffer and they are then likely to die.
Studies have shown that these particular marine algae respond best to
light from the blue end of the spectrum, which penetrates most
effectively into the sea. Specially designed lights for this purpose are
now available.

Artificial sea water for the aquarium can now be
made up easily, using special sea salt mixtures available for this
purpose. In order to maintain the water quality in the aquarium once the
sea anemones are present, a filtration system is essential.

At
first the water will be effectively sterile and the addition of a
starter culture will help to introduce beneficial bacteria here. These
in turn will colonise the filter, multiplying rapidly and ensuring the
breakdown of the waste products in the aquarium once it is established.
Again, advances in filter technology have helped to enable sea anemones
to be kept in good health in aquarium surroundings.

Water conditions

Sea anemones
can be found in waters ranging from 8°C to 28°C (46-82°F) in
temperature and it is vital to equilibrate the heater-stat in
their aquarium accordingly. Most marine aquarists favour tropical sea
anemones but keeping them too warm is likely to be harmful.

It is
also important to plan the layout of the aquarium carefully, so that sea
anemones which are solitary by nature do not come into contact with
each other when their tentacles are fully extended. If they are denied
adequate space, there may well be fatalities, but in suitable
surroundings, sea anemones can be long-lived. Their potential life
expectancy can be measured in decades in some cases.

Fish
generally should be excluded from an aquarium of this type, along with
algal eaters, such as cowries, because of the damage which they can
cause to the plant life in such surroundings. Feeding sea anemones is
actually quite straightforward however, with specialist foods available
for this purpose.

Choosing the sea anemones themselves in the
first instance can be more of a problem, simply because it is hard to
recognise illness in these creatures. Looking at the tentacles and
seeing these are fully extended, with no signs of shrivelling at their
tips, can be a helpful indicator. Similarly, the column which supports
the anemone on the rock should be stout and strong.